The main issue for Gravity has been casting. Angelina Jolie was originally cast in early 2010 as the female lead role of an astronaut assigned to a remote space station that is destroyed by satellite debris and is desperate to get back to her daughter on Earth. Jolie dropped out just as Robert Downey Jr. was cast as the space station team leader, but was later offered the role again. Jolie, again, said "no". Just as Sandra Bullock was finally cast as Jolie's replacement, Downey left the movie, ultimately being replaced by George Clooney.

"In the way that [Cuarón] pushed the narrative in Children of Men," explained del Toro. "Alfonso and [cinematographer] Emmanuel Lubezki are absolutely pushing a new boundary in filmmaking. [It's] completely mind-blowing and the way they're making that movie will, I think, forever change certain type of productions and the engineering and ingenuity of the machines they created to film that way is fantastic."

Gravity is reportedly about 60% CGI and will be converted to 3-D after shooting is finished. Del Toro said that the technology Cuarón is using is way ahead of its time.

I think what is incredible about what they did is they talked to David Fincher, they talked to Jim Cameron — I connected Jim and Alfonso for that. And what Alfonso is trying [to do in Gravity] is so insane and Jim said, well you know, look, you’re about five years into the future. When Jim said that it’s too early to try anything that crazy, they did it [anyway].

Del Toro continued to compliment Cuarón's work on the movie, comparing Gravity to the work of legendary director Stanley Kubrick.

I’m amazed at Alfonso the past few movies because he’s completely transformed himself. The thing Alfonso says [is] "This is the movie I should be doing when I'm in an armchair..." [Gravity is] incredibly well-calculated. Very human, if you know the story, it's incredibly human, but Kubrick-ian in [its] precision.